Check the camshaft timing. No, it's not necessary to pull the timing cover to do it- - - -you can watch the valve action and the timing marks on the front of the engine and get a very close estimate of whether you're a tooth off.

Remove the passenger's side valve cover, and watch the third pair of valves from the front (#6 cylinder). Turn the crankshaft slowly past TDC, and watch the valves. The exhaust valve should be in the process of closing, and the intake should be opening just as the timing mark passes TDC. At the same time, the distributor should be in the firing position for the #1 cylinder.

It's also possible you've got a mismatch between the timing cover timing pointer, and the mark on the vibration damper. Early model dampers and timing covers had the TDC mark at about the 2:00 position, while later ones would align with TDC at the 12:00 position, right behind the water pump. If you've got an early timing cover and a late damper, you're setting the ignition timing about 30 degrees late.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
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